This invention relates generally to optical spectrometers.
Optical spectrometers are instruments used to study intensity of light as a function of wavelength (where “light” herein refers to electromagnetic radiation generally and is not limited to the visual region of the electromagnetic spectrum). An optical spectrometer is composed of two basic elements. These are: a light filtering device, which allows the propagation of light within a selected portion of the energy spectrum; and a light sensor consisting of one or more photodetectors, usually a photodetector array. Typical photodetectors might be CMOS (complementary metal oxide semiconductor) capacitors or photodiodes which convert incident photons into electronic charge. A photodiode is a semiconductor device incorporating a PN junction, or PIN junction, operated in reverse bias. Absorption of photons with energies above the band gap of the device causes excitation of carriers across the band gap, resulting in generation of a current (the “photocurrent”).
In order to select a spectral region, conventional spectrometers rely on angular dispersion of light beams by prisms or diffraction gratings. To exploit the angular dispersion, the light needs to propagate over finite distances of the order of several wavelengths. This need for spatial propagation limits the extent to which the energy filtering part of a spectrometer can be scaled down in size. This, in turn, has limited further miniaturization of the entire optical spectrometer and prohibited the integration of spectrometers in other, more complex systems.